The present invention relates to an oil and gas industry, and, more particularly to a self-elevating offshore structure that can be used for developing and production of wells in an offshore location. Even more particularly, the invention relates to a truss structure that can be used in a self-elevating unit without the need to provide a buoyant hull.
Self-elevating units are extensively used in the oil and gas industry, and numerous designs of such structures are available from shipyards and naval architects. Conventionally, self-elevating units have a plurality of supporting legs, either of tubular or trusswork constructions and a buoyant hull of a barge-type construction. Conventionally, the unit transports itself to a deployment site, the legs are elevated above the hull and the unit is floated on its own buoyant hull. During transport to a deployment site for the current application, the legs are elevated above the truss structure and the truss unit is loaded onto transport barges. Once the unit is delivered to the site of the operation, the legs are lowered and embedded into or engaged with the ocean floor.
Conventional installation operation continues with the truss work that is still in rigid connection with the transport barge being elevated to impose loads onto each spudcan or footing by lifting the weight of the transport barge. Additionally the hull of the transport barge can be ballasted with seawater to apply the necessary loads to the legs to simulate the loads that can be achieved in the operational conditions. Once the preloading of the footing is established, the water is drained from the transport barge hull.
The rigid connections between the trussed deck of the elevating unit and the transport barge are removed, thereby leaving the transport barge hanging on a tension only connection. The hull of the transport barge is lowered back into the water and completely disengaged from the truss deck unit. The truss deck unit is finally elevated to the operational height above the anticipated wave action, and the unit is ready for the offshore operations.
If the offshore unit is used for production operations, the owners avoid installation of the equipment in the hull due to a potential of an explosive atmosphere in confined spaces. As a result, the majority of the hull remains unused during the production operations. Eventually, the buoyant hull of a conventional unit becomes a maintenance problem.
The present invention contemplates elimination of drawbacks associated with the prior art and provision of an offshore structure that does not use a buoyant hull.